1. Field of the Invention
The present invention relates to mobile radio telephone systems and, more particularly, to a method and apparatus for generating toll ticketing records for the billing of calls within a mobile telephone system.
2. History of the Prior Art
when a mobile subscriber originates or receives a phone call in a mobile telephone switching office ("MTSO") (also referred to as Cellular System or exchange), that MTSO collects charging data during the call and outputs it in the form of a call billing record (a "toll ticketing record" or a TT record) at the end of the call. Such charging data may include, for example, a call identification number, the mobile station number, the subscriber number, the date, the number called and the time duration of the call. These billing records are then stored on a recording medium such as a magnetic tape or a hard disk and are later processed to produce telephone bills that can be sent to the subscriber.
When two or more MTSO's serve adjacent cellular radio coverage areas and share a geographical boundary, existing functions within the systems may allow calls to start in one exchange and terminate in another. When a moving mobile station having a call in progress crosses the boundary between two adjacent systems, the call is "handed over" from the initial exchange ("anchor exchange") to the second exchange ("serving exchange"). Thus, calls are handed over not only from cell to cell during the normal course of operation within a cellular communication exchange but also from one exchange to another. The process of handing over calls from one exchange to another is called an interexchange handoff or an intersystem handoff.
If the call with which a mobile is engaged occurs entirely within the same MTSO that MTSO is entitled to the entire revenue from the use of its cellular facilities by the mobile. However, if the mobile travels through and uses the cellular communications facilities of more than one MTSO, each system should receive a proportional share of the revenues from that call.
While there are prior art systems for collecting and forwarding call charging information from a mobile home exchange to a visited exchange in which a roaming mobile may originate a call, such as that shown in U.S. Pat. No. 4,698,839, even if the anchor exchange produces TT records for calls which are handed over to a second, and perhaps subsequent exchange, these records do not indicate the time during which the mobile was present in the serving exchange. Furthermore, in the call billing record currently produced by the anchor exchange, there is no indication whether a call went through an interexchange handoff or not. Therefore, revenues which should be owed to the serving exchange for the use of its cellular communications facilities are not properly recorded in the call billing records and therefore that exchange does not derive a fair share of the revenues received from the mobile for handling a portion of such calls.
Accordingly, it would be desirable to have a method and system within the anchor exchange of a cellular call for generating a record for the operator of that exchange, as well as all other exchanges to which the mobile is handed off during the call, of the time at which a call is handed off to a serving exchange and the identity thereof.